1. Field of the Invention
The present invention relates to a tower foundation system for large, heavy and bulky towers such as wind turbine towers and steel chimneys, said system comprising a foundation and a bottom section of a tower, which bottom section is connected to the upper part of the foundation.
The invention relates to tower foundation systems in general. However, in the following a tower foundation system is described in relation to a wind turbine tower.
2. Description of the Related Art
Modern wind turbines tend to get bigger in order to produce more power. The length of the wings may exceed 60 m and the height of the tower may exceed 100 m, thus increasing the load on the foundation tower holding the wind turbine.
Traditional tower foundations consist of a cast gravity foundation element provided with an embedded steel cylinder with a 300-500 mm flange at the bottom of steel cylinder for transferring the load from the steel cylinder to the concrete. A machined flange is arranged on top of the steel cylinder and is prepared for connection to a bottom section of the wind turbine tower. The steel cylinder is traditionally cast into the cast gravity foundation element with reinforcement elements protruding through the steel cylinder. The embedment depth of casting compared to the diameter of the steel cylinder need to have a certain value in order to ensure proper securing of the steel cylinder to the foundation, i.e. sufficient load transfer from the steel cylinder to the foundation.
To ensure that the tower foundation sustains the load and stress from the tower, the steel cylinder is cast deep into the gravity foundation to transfer the load to the foundation. The curing period of the standard concrete is long, and casting of the entire foundation comprising the embedded steel cylinder is complex and time consuming. Thus the costs of the foundation are relatively high compared to the total assembly costs of the wind turbine.
The steel cylinder having a top flange and a large bottom flange requires transportation to the wind turbine erection site, where it is to be embedded into the concrete gravity base. Logistically this is a challenge increasing the costs of the project.